The present invention relates to a radial piston pump. More particularly, it relates to a radial piston pump in which base portions of pistons are in sliding engagement with an eccentric of a shaft of the pump.
Radial piston pumps in which base portions of pistons are in sliding engagement with eccentric of a pump shaft have been proposed in the art. In the known radial piston pumps, the base portions of the pistons are of one piece with the latter and are constituted by the same material. Since under the action of great bearing forces this material tends to wear, the piston is to be hydraulically equalized for reducing bearing forces between the piston base portions and the eccentric. For this purpose, the piston is provided with radial passage which communicates an inner chamber of a pump housing with the piston base portion, whereas in the eccentric region of the piston base portion a recess is provided, which substantially corresponds to the contact surface of the piston. Such hydrostatic unloading of the piston with the piston base portion and corresponding reduction of the pressure exerted by the piston base portion to the eccentric requires very high manufacturing accuracy, inasmuch as otherwise a working fluid enters the region between the piston base portion and the eccentric and, in addition to increased leakage, makes the hydrostatic unloading ineffective. This results in fast wear of the contact surfaces of the eccentric and piston base portions which are movable relative to one another.
It has been also proposed to produce the piston base portions as separate members, and to make the piston base portion of a material having good bearing characteristics, such as of a bronze alloy. In this case, the piston base portion is secured to the piston by means of screws. An additional hydrostatic unloading of the pistons with the piston base portions is thereby not needed. However, this construction also requires accurate manufacture in order to reduce the sliding friction between the piston base portions and the eccentric, since otherwise cavities formed on the piston base portions and the eccentric would result in fast wear of the same. The above-mentioned known bearing of the piston base portions with the eccentric requires also very fine filtering of the oil or the working fluid, in order to halt the wear of the surfaces of the piston base portions and the eccentric sliding relative to one another, in narrow limits so as to assure a practically justified service life of the bearing.